Tingling/itching near the end of feeding

Hi ladies! FTM here. I have a 1wo who exclusively breastfeeds. My supply seems to be establishing very well; I start feeling engorged about every 2 hours, and my milk starts pouring as soon as I or he touches the boob (sometimes before lol). Usually about 15-20 minutes into a feeding, the boob that's being nursed gets a sharp tingling/itching sensation. Is this let-down or a signal that the boob is "almost done"?  He typically nurses for about 25-40 minutes at a time. I don't want to detach him too soon if it's let-down, but if it's an end signal I can know to switch him to the other side if he's still suckling.